This invention relates to electrical connectors and in particular to insulation displacement contacts which are commonly mounted in connecting blocks for connecting insulated wires either to contacts on a wiring block or to a second set of wires. The Invention also relates to connecting blocks for housing insulation displacement contacts.
Insulation displacement contacts are of particular applicability to the voice and data communications industry. There have been many proposals for insulation displacement contacts (IDC) in the past. However. all prior proposals suffer from one or more of number of disadvantages as will be described.
The basic function of a connector block is to house a number of insulation displacement contacts, normally 4 or 8. The individual contacts provide at one end a pair of contacts for attachment either to a wiring block or to individual wires and at the other end a pair of contacts for receiving an insulated wire. The contacts are disposed in a manner which ensures that the insulation around the wire is stripped away or displaced as the wire is fed between the contacts. Commonly, this has been achieved by a cantilevered split beam where the two beam halves are displaced by a distance less than the width of the insulation of the wire with which the connector is to be used. The open ends of the beams are usually shaped so that the wire can be guided between the beam halves or tynes and a slot or opening is provided to retain the wire, with its insulation displaced, in contact with the connector and to give the tynes a degree of flexibility.
U.S. Pat. No. 4,964,812 (Siemon) discloses an IDC which comprises two opposed cantilevered beams each of which comprises a pair of tynes and each of which extends from a central portion. Each tyne pair is separated by an elongate opening along a part of its length and is formed from an original cantilevered beam by shearing along a shear axis which forms the cutting surface for cutting the insulation on a wire. The shear axis is conveniently the longitudinal axis of the cantilevered beam. This shearing produces a closed gap between the tynes of a beam. However, a secondary closing action is necessary to achieve a satisfactorily small gap between the tynes. This is achieved by a coining operation performed on the outside edges at the base of the tynes and decreased coin surfaces pre-load the beam elements whilst maintaining clean contact surfaces and raising the contact force to a level where it is sufficient to penetrate the insulation on small wires.
The need for a secondary operation to close the slot to the required dimension is undesirable and arises from an attempt to overcome problems with beam stiffness by increasing contact thickness.
The performance of a split beam contact is determined by the stiffness of the beam, which is itself proportional to the cube of the contact width in the direction of flexing. The requirement for contact stiffness is in direct conflict with the requirement that the IDCs have the smallest possible pitch so as to minimise installation space and connector block width.
The solution proposed in U.S. Pat. No. 4,964,812 requires the secondary closing operation because the beam stiffness problem has been overcome by increasing contact thickness rather than width. The result is an IDC which is difficult to manufacture.
A similar approach has been taken by A T & T in their 110 series connectors, for example the 110C-4. The displacement contacts for the connectors are described in a number of U.S. patents, for example U.S. Pat. No. 3,611,264 (Ellis), U.S. Pat. No. 3,798,587 (Ellis) and U.S. Pat. No. 4,118,095 (Berglund).
The contacts described in all these documents suffer from the same problems as the Siemon patent due to the attempt to solve beam stiffness problems by increasing contact thickness.
It has been proposed to overcome the requirements of a stiff beam and a narrow contact by producing a wide beam and rotating it in the connecting block by an angle of 45.degree. to the central block axis. However, this approach still requires that a narrow slot is produced between the tynes, requiring a secondary closing operation and necessitating a wider moulding than the A T & T or Siemon solutions.
U.S. Pat. No. 4,295,703 (Northern Telecom) proposes a solution in which the gap between tynes is wide and the contacts are arranged in staggered rows. Although this alleviates the problems of closed gap connectors such as the A T & T and Siemon connectors it has the disadvantage that it requires a complex wire insertion tool to feed wires between the tynes and also a connecting block which must be made wider than is desirable to accommodate two rows of contacts.
A problem encountered with connector blocks which house insulation displacement contacts is end wall thickness. As the blocks usually house four or eight contacts it is usual to arrange a number of blocks side by side along a wiring block. The wiring block has a plurality of IDC receptors which are spaced apart evenly. End walls of adjacent connector blocks which abut one another tend to have a combined thickness which is too great for the spacing between the receptors on the wiring block.
Merely reducing the thickness of the end walls can lead to a structure which is too weak. U.S. Pat. No. 4,964,812 mentioned previously overcomes the problem by using free floating insulation displacement contacts and by displacing the end contacts away from the end wall by about 0.005 inches (0.0127 cm). This enables the thickness of the end wall to be increased by about 30% and reduces end wall breakages. However, it does have the problem that it relies on very high manufacturing tolerances and on the use of free floating contacts.
GB-A-2112217 (Broomadit Limited) discloses a system in which the tynes are folded around a central axis. The tynes are held firmly in place in the housing.
The present invention aims to overcome or alleviate the above mentioned problems.